Observation of a new Bs π state

Abstract

We report the observation of a narrow structure, X(5568), in the decay sequence X(5568) &rarr; Bs &pi;&plusmn;, Bs &rarr; J/&psi; ϕ, J/&psi; &rarr; &mu;+&mu;&minus;, ϕ &rarr; K+K&minus;. This is the first observation of a hadronic state with valence quarks of four different flavors. The mass and natural width of the new state are measured to be m = 5567.8 &plusmn; 2.9 (stat) +0.9&minus;1.9 (syst) MeV and &Gamma; = 21.9 &plusmn; 6.4 (stat) +5.0&minus;2.5 (syst) MeV, and the significance including look-elsewhere effect and systematic uncertainties is 5.1&sigma;. The observation is based on10.4 fb&minus;1 of ppbar collision data at 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.</p